Recently, it has been performed to print an image on a sheet using erasable coloring agent such as ink including leuco dye, in order to erase the formed image and make the sheet to be reused by an image forming apparatus such as an MFP (Multi Function Peripheral). On the other hand, in case that various images are printed on a sheet, the necessity to administer the sheet or to administer the image data has been generated from a standpoint of security, from the time of forming the image to the time of decoloring, recycling or disposing the sheet.